1. Field of the Invention
The present invention relates to the calculation of charges for calls made from a mobile communications device in a cellular mobile communication system.
2. Description of the Related Art
In a wired network, the charge assessed for a call depends on whether the call is a local call, a trunk call or an international callxe2x80x94i.e. a geographically defined callxe2x80x94or is, on the other hand, a call to a service number. Thus, when dialing the number of a called subscriber, the calling subscriber already knows the principles or basis on which the cost or price of the call will be calculated.
The rules or principles used in a wired network for calculating the call price cannot be directly applied in mobile telephone networks. This is because the mobile subscriber is not tied to a given locality, whereas the called subscriber may be a locality-dependent wired network subscriber, or a mobile subscriber in the same mobile communication network, or a mobile subscriber in another operator""s mobile communication network. Within the mobile communication network, no distinction is made between local and long-distance calls in respect of pricing; moreover, in contrast to the wired network, the called subscriber may in some cases or systems be required to pay a portion of the price of a received call.
In mobile communication networks, a difficulty in locality-dependent determination of call pricing is that the exact locality of neither the calling subscriber nor the called subscriber is known. To provide an understanding of the principles by which call pricing is calculated, the call setup process in a mobile communication network will now be described in general outline form by reference to FIG. 1.
When a calling subscriber in cell a1 within location area 1 under mobile switching center MSC1 initiates a call to a subscriber in location area 2 under another mobile switching center MSC2, he or she will dial the MSISDN (Mobile Subscriber International ISDN) number of the called subscriber on his or her mobile station MS-A, which sends it in a message to the base transceiver station 1 (step 1). Upon receiving the message, MSC1 determines whether the request can be accepted. As a part of this determination, the subscriber data of the calling subscriber are retrieved from the visitor location register VLR1 associated with MSC1 at which they have been stored in conjunction with the standard location updating procedure. If the request is accepted, the mobile switching center MSC1 will send to the home location register HLR an enquiry containing the called subscriber""s MSISDN number (step 2). Based on that number, the HLR retrieves the data for the called subscriber, which indicates that the called subscriber has roamed to visitor location register VLR2. Next, the HLR sends the IMSI (International Mobile Subscriber Identity) data to visitor location register VLR2, asking the latter to provide it with the roaming number (step 3), whereupon VLR2 sends the roaming number MSRN (Mobile Subscriber Roaming Number) to the home location register HLR (step 4), from which it is further sent to MSC1 (step 5).
After this, the call can be routed from mobile switching center MSC1 to mobile switching center MSC2 on the basis of the MSRN received from VLR2 (step 6). Upon receipt of the start message, the mobile switching center MSC2 of the called subscriber retrieves the subscriber data for the called subscriber from the associated VLR2. From that subscriber data, MSC2 learns the location area LAI-2 of the called subscriber, so that MSC2 is able to send a paging message tot he called subscriber""s mobile station via the appropriate base station controller 2 (step 7) for the cells b1, b2, b3 of the location area in question. After the called subscriber""s mobile station MS-B has responded to the paging message, the call to the called subscriber is finally set up. From the foregoing, it will be apparent that only after the called subscriber""s mobile station has responded to the paging message is the relevant mobile switching center MSC2 informed of the called subscriber""s current cell level location.
The mobile switching center may also be linked to a service switching point SSP of an intelligent network IN to allow connections from the mobile communication network to the intelligent network. Through an intelligent network, a wide variety of services can be offered to the subscribers of the mobile communication network, including services such as xe2x80x9cfollow-mexe2x80x9d call diversion, call rerouting distribution, premium rate call pricing, etc.
In a state-of-the-art mobile communication network, the most basic rule of call charging is that the calling subscriber is charged for the connection between him or her and the home network of the called subscriber, while the called subscriber is charged for the connection between his or her current locality and his or her home network.
To increase flexibility in connection with the application and assignment of billing rules and principles, a known method is to set a special billing parameter that allows calls made from the subscriber number associated with the parameter to be billed at a lower rate than normal at times when the load on the mobile communication network is low and, correspondingly at a higher rate when the load on the mobile communication network is high. This parameter thus creates a time-dependent call charging principle, but in other respects the pricing of calls follows the above-mentioned principles.
Another known practice is to charge a lower price for calls between a mobile station and a specified wired network telephone than for normal calls. The latter can be implemented by assigning for all subscribers to the service a common service number, e.g. 020100, as the called subscriber number which directs the call to an intelligent network. In the intelligent network, a service program searches a database to find the called subscriber number that is associated with the calling subscriber number, and the call is then automatically routed to the database-stored number.
A comparison of the principles of call price calculation used in mobile communication networks with those used in wired networks reveals certain problems. Since all cells are the same as concerns call charging within to the mobile communication network, it is difficult to offer various user groups any other principles of call price calculation than, for example, the aforesaid price variations based on time-of-day. At present, there are no special call price calculation principles applicable to calls within the same cell or to calls between specific cells. However, it would be attractive for a mobile telephone network operator to be able to provide various services dependent on the locality from which the call originates and/or where it terminates. Such services may for example include locality-dependent pricing schemes.
Patent specifications WO-96/20570 and WO-96/20571 disclose solutions for determining the principles of call price calculation. The price calculation principles can for example be improved by identifying a specified or predetermined cell or number of cells of a mobile telephone network as a special cell group. During call setup, the mobile switching center or a service control point SCP in an intelligent network analyses the call to determine whether the cell in whose area the calling subscriber is located and/or the cell in whose area the called subscriber is located belong(s) to the group of such xe2x80x9cspecialxe2x80x9d cells. When the calling and called subscribers are located in cells belonging to different switching centers, data regarding the cell of the called subscriber is transmitted to the switching center of the calling subscriber, or to an intelligent network, before a voice connection is established. In this way it is possible to vary the call charging rates to be applied on the basis of whether the subscribers are or are not located in a group of these special cells.
Patent specification WO-96/34499 describes a system in which the subscribers are divided into normal subscribers and xe2x80x9cfixedxe2x80x9d subscribers. A normal subscriber may start a call in any cell, whereas a fixed subscriber has only limited access to the network from a subscriber area comprising one or more predetermined cells. When a fixed subscriber is at the boundary of his or her area, the call is forcibly directed to the base transceiver station of the subscriber area, if possible.
These prior art solutions allow the application of more fine-grained call charging principles than those generally used. A feature common to these solutions is that the right to a differently priced call is determined by reference to the cell in whose area the subscriber is physically located at the time of the call, i.e. according to the base transceiver station that connects the subscriber to the network. This aspect of these solutions results from the fact that the metering record generated at the start of the call includes, among other data, an identifier of the base transceiver station via which the connection is set up, and the base station identifier in turn reveals whether the base station belongs to a group of special cells. In other words, the base station identifier functions as a factor that ultimately determines the price of the call.
However there is a problem associated with these prior-art solutions. In most mobile telephone systems, it is the network that makes the decision as to which base station is to be used to transmit the subscriber""s calls. When the subscriber is in the fringe area of a cell in which a lower call charge is applicable, the network may repeatedly instruct the mobile station to perform a handover between two base stations, which means that the calling end of the connection alternates between the base station of a xe2x80x9cless costlyxe2x80x9d cell and the base station of an adjacent (and more expensive) cell. If the adjacent cell is not one of the cells where a lower call charge is applicable, then the call price will vary during the same call as the connection is repeatedly handed over from one base station to another, the call charge being thus lower at one moment and higher at the next, without the subscriber having any opportunity to influence the situation in any way.
One proposed solution to this problem is to assign to the mobile station some of the handover control functions between base stations. In the idle state, the mobile station would remain for as long as possible in signaling contact with a cell applying a lower call charge when in the fringe area of the cell; in other words, the mobile station would remain xe2x80x9changingxe2x80x9d in the cell even when a neighboring cell would provide a better quality or more reliable connection. During a communication connection, too, the mobile station would continue hanging in the old cell when in the area of another cell, and it would inform the networkxe2x80x94e.g. in conjunction with a change of base station or the call setup procedurexe2x80x94that it gives preference to the old base station which provides less costly service over or instead of other base stations.
This proposed solution, however, exhibits the drawback of increased co-channel interference which arises because, when the communication connection is forcibly maintained via the base station of a less expensive cell although the mobile station is located in the area of an adjacent (but more expensive) cell that would provide a better connection, the mobile station has to use a higher transmission power to compensate for the signal attenuation caused by the longer transmission distance. As a consequence, the mobile telephone causes interference with other mobile stations using the same frequency and that are communicating at the reuse distance of this frequency. Another drawback is that changes need to be made in certain network components, such as the base station controller and the telephone itself, to implement it; specifically, changes must be made in at least the handover criteria and controlling algorithm.
Another solution proposed to deal with this problem is to have information presented on the display of the mobile station in its idle state to indicate the particular cell in whose area the mobile station is currently located. The idea is to thereby provide the subscriber with information that he or she can use as a basis for intentionally moving into the area of a cell with a lower call charge when the subscriber is at or near the boundary between cells. A drawback of this solution, however, is that because the billing record is generated at the beginning of the call when the telephone is already in the active state, the subscriber may unintendedly move on to the area of a cell with a higher call charge rate during the call setup procedure based on the information seen on the display before transmission of the call setup request that the mobile station is still located in the area of a less costly cell.
It is therefore the object of the present invention to achieve a system that is free of these drawbacks of prior art systems and that does not result in co-channel interference. In such a system, determination of the location of a mobile station should be implemented in a manner that allows a call started from a xe2x80x9cspecialxe2x80x9d cell to continue being charged at the rate applicable to that cell even if the mobile station should move on to a cell with a normal or increased charging rate during call setup. A further object is to ensure that, even if call setup is initiated in a cell with a normal charging rate but a time interval earlier the mobile station had been in a special cell, the call can still be charged at the rate applicable to the special cell. The length of time of the time interval should also be adjustable.
Yet another object of the invention is to provide a system in which the area of a specially priced call is not dependent on the cell coverage area but may instead consist of any geographic area; such an area may even consist of a portion of one cell and a portion of another cell. Location of the mobile station should therefore be independent of the information transmitted by the base stations.
In accordance with the invention, the mobile station is provided with a first object, i.e. a locator object, which determines the location of the mobile station. The location function can be carried out to resolve to the accuracy of a cell or to a sub-area of a cell, making use of the existing properties of the mobile communication system. By utilizing location methods external to the mobile telephone system, completely cell-independent location can be achieved. The location function is executed at certain predetermined intervals. The mobile station also contains a stored list of cells and/or areas in which a special charging rate is applicable. The locator object monitors the calls originating from the mobile station and, when it detects the start of a call, it determines whether the mobile station was in a cell or area with a special charging rate at the time at which the location function was last executed. If so, then the object will inform the network that the call is entitled to a special rate. Because the last location function has been executed before the commencement of call setup, charging of the call at a special rate is possible even if the mobile station has subsequently moved some distance into the area of a cell applying a normal rate. Channel allocation is carried out independently of location in accordance with the normal procedures in the system, which means that co-channel interference is avoided.
One of the network elements is provided with a second object, i.e. a billing object, to which the first object sends information indicating whether the call has been started from a cell or area in which a special rate is applicable. The second object receives the billing records generated by the mobile switching center and compares the call-specific data in those records with the data sent by the first object. In this way, the second object can identify in the billing records those calls that are entitled to a special rate, even if the mobile station has moved during call setup from the original cell or area into a cell in which another charging rate, e.g. a higher rate, is applicable.
Cells allowing the application of a special rate can be divided into groups of cells or areas, and each of the groups may have a different rate applicable in that group. Thus, when the final telephone bill is being compiled, the rate applicable in the special rate group can be checked and the call charges determined accordingly.
The locator object may send to the network the data concerning a call entitled to a special rate either during the call or, alternatively, it may collect such data for a desired length of time and send the data all at once to the billing object. However, the latter method leads to increased difficulty in generating the telephone bill if the data are received after the call records received during the billing period have been subjected to post-processing.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which, reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.